This application is based upon and claims the benefit of priority of the prior Japanese Patent Application 2003-307006 filed on August, 29.
The present invention relates to a control apparatus for an internal combustion engine that controls electric power supplied to an ignition coil with a power supply amount determined based on a resistance characteristic value of the ignition coil that represents either a resistance value of the ignition coil or a physical quantity having correlation with the resistance value.
The power supply amount supplied to an ignition coil of an internal combustion engine should be an appropriate value within an allowable current range between a maximum current value and a minimum current value. The maximum current value of the ignition coil is generally defined considering protection of an igniter. The minimum current value of the ignition coil is defined considering the possibility of firing failure.
In controlling the electric power supplied to the ignition coil, the current flowing in the ignition coil is dependent on a resistance value of ignition coil. The resistance value of the ignition coil varies depending on the temperature of the ignition coil. Accordingly, even when the power supply control for the ignition coil is performed in the same manner, the current flowing in the ignition coil varies in accordance with the ignition coil temperature. The power supply time for the ignition coil should be changed in accordance with the temperature change in the ignition coil so that the power supply amount to the ignition coil is always within the allowable current range.
The Japanese patent application Laid-open No. 08-338349 discloses a control apparatus which detects the temperature of intake air introduced into an internal combustion engine, an outside air temperature, and the temperature of cooling water flowing in the internal combustion engine. This control apparatus makes a judgment based on these temperature data as to whether the ignition coil temperature is high or low. Then, the control apparatus changes the power supply time required for the ignition coil with reference to the ignition coil temperature, so as to optimize an electric power amount supplied to the ignition coil.
In general, an actual ignition coil generates the heat in response to electric power supplied form a power source, receives the heat from an internal combustion engine, and releases the heat to the outside. Thus, the ignition coil temperature momentarily varies due to these factors. It is therefore difficult to accurately calculate a power supply time reflecting an actual temperature of the ignition coil.
As described above, it may be difficult to accurately calculate a power supply time reflecting the ignition coil temperature. Accordingly, in the case that the power supply amount supplied to the ignition coil exceeds the above-described allowable current range, the current supplied to the ignition coil is regulated with a specific hardware (e.g., regulator). However, the above-described allowable current range is dependent on characteristics of each ignition coil. It will be necessary to develop the regulators so as to be desirable for individual ignition coils.
Furthermore, the surplus of regulated current usually changes into the thermal energy. The temperature of a portion positioned adjacent to the regulator will increase. Especially, a control apparatus incorporating an ignition module will produce a significant amount of heat from the ignition module which serves as a heat generating source. Suppressing such a temperature increase is an important issue to be attained in designing the control apparatus.
Furthermore, in performing the power supply control for the ignition coil, it is generally difficult to appropriately control a power supply amount according to a resistance characteristic value of the ignition coil that represents either a resistance value of the ignition coil or a physical quantity having correlation with the resistance value.